1. Field of the Invention
The present invention relates, in general, to gear reduction devices and, more specifically, to power seat adjusters for vehicle seats employing gear reduction devices.
2. Description of the Art
Gear reducers or gear reduction units are employed with rotating devices, such as motor output shafts, lead screws, drive shafts, etc., to reduce the speed of rotation of one shaft or element to a lower speed of rotation of a coupled or driven element. Gear reducers are available in a variety of configurations and provide gear reductions of between 1:2 to 1:1000 and more.
One application of gear reducers is in a power seat adjuster for a vehicle seat which provides for selective fore and aft, up and down and/or seat back reclining features. A typical power seat adjuster carries an upper support frame or support members which engage and support the seat bottom of a vehicle seat. The upper support members are mounted on first and second, spaced track assemblies, each formed of an upper track which is connected to the upper support frame and slidably mounted in a lower track fixedly anchored to the vehicle floor. A drive mechanism, typically formed of a bi-directional electric motor mounted on the power seat adjuster, rotates a pair of shafts extending outward from the motor to a gear assembly or gear box mounted on each upper track. Each gear box includes a gear reducer unit to reduce the high speed of rotation of the shaft to a lower speed of rotation of a lead screw which is coupled to each upper track and which is rotatively driven by the gear box.
While such a power seat adjuster provides smooth selective positioning of a vehicle seat, it is well known that a considerable amount of noise is generated in a typical power seat adjuster due to the high speed of rotation of the shafts, particularly when a flexible shaft is employed. One drive motor used for horizontal fore and aft positioning of the seat is typically mounted between the spaced track assemblies with flexible shafts extending outward from opposite sides of the motor to the gear boxes mounted on the track assemblies. Both shafts rotate at the same time thereby doubling the noise generated by rotation of such shafts.
Thus, it would also be desirable to provide a gear reducer which has multiple numbers of gear teeth in engagement at any one time so as to provide a desired amount of torque while enabling the use of low strength, low cost materials for such gears. It would also be desirable to provide a gear reducer which is quiet in operation. It would also be desirable to provide a gear reducer which prevents any back drive. It would also be desirable to provide a gear reducer which reduces the noise generated by rotation of a drive shaft when the gear reducer is employed in a vehicle power seat adjuster. Finally, it would also be desirable to provide a gear reducer which may be directly connected to or integrally formed with an electric drive motor so as to reduce the size of the mechanical components of a vehicle power seat adjuster.